In general, a diaphragm-type electromagnetic valve has a valve structure as a two-port valve as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2001-304436. This diaphragm-type electromagnetic valve is configured to open and close a flow path by causing a diaphragm to be in contact with or to be separated from a valve seat that is formed in a half way of the flow path connecting a supply port with an output port. In addition, the diaphragm-type electromagnetic valve is configured to be operated to open and close the diaphragm by means of an internal pilot type solenoid-operated pilot valve.
Oxygen condensation is one of intended purposes of such a diaphragm-type electromagnetic valve. The oxygen condensation is performed, as illustrated in FIG. 7 by marks for example, by forming an electromagnetic valve assembly while mounting first to fourth diaphragm-type electromagnetic valves 1a, 1b, 1c, and 1d, respectively, on a manifold base 2 provided with a flow path 3 for use in supplying in a lump, a flow path 4 for use in discharging in a lump, and two of flow paths 5a and 5b for use in output. The oxygen condensation is performed by respectively connecting first and second tanks 6a and 6b serving as containers for use in nitrogen adsorption with the aforementioned two of flow paths 5a and 5b for use in output. The oxygen condensation is performed by supplying compressed air to or discharging the same from the aforementioned tanks 6a and 6b, while selectively and relevantly operating the aforementioned four diaphragm-type electromagnetic valves 1a, 1b, 1c, and 1d. 
However, for example, when the compressed air is supplied to the second tank 6b by switching the second diaphragm-type electromagnetic valve 1b from an illustrated closed-valve position to an open-valve position in a condition where the first diaphragm-type electromagnetic valve 1a is again switched to an illustrated closed-valve position, and a filled-up condition is held after the compressed air is supplied to the first tank 6a by switching the first diaphragm-type electromagnetic valve 1a from an illustrated valve-closed position to a valve-open position, and the compressed air is filled up, air pressure in the aforementioned flow path 3 for use in supplying in a lump is temporarily lowered. Thereby, the diaphragm of the first electromagnetic valve 1a is sometimes temporarily pressed open by an operation of adverse pressure from the first tank 6a. This can be said for a case when compressed air is supplied to the first tank 6a by means of the first diaphragm-type electromagnetic valve 1a in a condition where the compressed air is filled up and held in the second tank 6b by means of the second diaphragm-type electromagnetic valve 1b as well.
Thus, the diaphragm-type electromagnetic valve sometimes performs unstable behavior due to an operation of adverse pressure from a load depending on a direction for use. Therefore, this results in lowering of reliability or accuracy of fluid-controlling devices, and there is a demand for early improvement therefor.